TABLE 1.

The advantages and disadvantages of selected platforms to study the mechanics of the metastatic cascade.

Metastatic cascade	Platform	Description	Advantages	Disadvantages	Key papers
Tumor Microenvironment	2D Nano-spacing	Block copolymer micelle nanolithography (BCMN) and peptidomimetics are used to synthesize nano-spaced peptide-coated particles on a culture substrate	ECM ligand density can be highly controlled Single-cell resolution	2D cultures do not recreate 3D in vivo cell-cell and cell-ECM interactions	Young et al., 2020 Amschler et al., 2018
	3D Hydrogels	Tuneable semi-synthetic hydrogels such as GelMA and alginate-based interpenetrating networks utilize UV or Ca2+ crosslinking to modulate substrate stiffness (and pore size in GelMA)	Replicates cell-cell and cell-ECM interactions On-demand (temporally and spatially) tuneable stiffness/pore size Elastic and viscoelastic options	Reduced imaging quality/ease of imaging with increasing sample thickness Unable to replicate the diversity of natural ECM	Panciera et al., 2020 Joyce et al., 2018 Kim C. et al., 2020 Peela et al., 2016
Invasion	3D Hydrogels	Tuneable natural hydrogels such as collagen type I or reconstituted basement membrane are thermally polymerized. Substrate stiffness can be controlled by adjusting protein concentration and gelation temperature	Tuneable soft stiffness’s Native ECM proteins Viscoelastic properties close to in vivo conditions	Tuneable stiffness typically does not cover the complete physiological range Cannot control pore size	Chaudhuri et al., 2014 Wullkopf et al., 2018
	Microchannels	Soft lithography is used to fabricate microchannels of varying dimensions and topographies by casting polydimethylsiloxane over silicon wafers/molds	High spatial resolution Relatively cheap Routine microscopy compatible	Reduced substrate stiffness tuneability Unable to recreate true heterogeneity of tissue topography	Holle et al., 2019 Ma et al., 2018 Microchannels created in collagen address this, see Mosier et al., 2019
Intra/Extravasation	Co-culture Microfluidics	Soft lithography is used to fabricate perfused microfluidic chips designed to accommodate different cells types that can communicate and interact through media or hydrogel reservoirs	Physiological culture of endothelial cells in platforms with flow Inter-cellular communication	Increased cost, preparation time, and resource demand Reduced data resolution with increasing complexity	Chen et al., 2013 Nguyen et al., 2019
	Subnuclear Microchannels	Soft lithography or glass etching allows for the fabrication of subnuclear constriction challenges. Nuclear constriction topographies include periodic pinch-points and restricted channels	Highly controlled constriction dimensions Single-cell resolution with manipulability	Limited control of perceived substrate stiffness Increased preparation time and required resources	Raab et al., 2016 Sima et al., 2020
Circulating Tumor Cells	Microfluidics	Soft lithography-fabricated microfluidic chips are connected to pumps that circulate cell media and thus exert shear stresses on cells and/or maintain them in suspended culture	Application and control of fluidic shear stress Reduced handling during experimentation	Lacking interaction with native blood/lymph cells Live-cell imaging resources Increased preparation time	Zhang et al., 2014 Fan et al., 2016 Can be utilized for real-time deformability cytometry see Otto et al., 2015
	Metastasis-on-a-chip	Composite platforms incorporating a combination of the above platforms (i.e., 3D encapsulated cell types and perfused microfluidics) to study the metastatic cascade in an integrated fashion	Incorporation of many in vivo variables Multi-system chip scalability	Reduced data resolution with increasing complexity Optimizing culture media Increased preparation time and required resources Low through-put	Rajan et al., 2020b Aleman and Skardal, 2019 Hassell et al., 2017